Download or read book Aquatic Bioindicators of Late Holocene Environmental Change on the South Central Tibetan Plateau written by Paula Gabriela Echeverría Galindo and published by . This book was released on 2021 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Holocene Paleo Environmental Reconstruction in Central Tibetan Plateau Inferred from a Lacustrine Sediment Record written by Man-Ching Cheung and published by Open Dissertation Press. This book was released on 2017-01-27 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: This dissertation, "Holocene Paleo-environmental Reconstruction in Central Tibetan Plateau Inferred From a Lacustrine Sediment Record" by Man-ching, Cheung, 張敏青, was obtained from The University of Hong Kong (Pokfulam, Hong Kong) and is being sold pursuant to Creative Commons: Attribution 3.0 Hong Kong License. The content of this dissertation has not been altered in any way. We have altered the formatting in order to facilitate the ease of printing and reading of the dissertation. All rights not granted by the above license are retained by the author. Abstract: Previous studies on reconstructing the paleoclimate on the Tibetan Plateauare commonly based on a single proxy, and have thus limited the usage of their results. Therefore this study was designed firstly to evaluate the applicability of organic carbon isotopes from modern plants in the Tibetan Plateau as a paleo-environmental proxy, and secondly to apply palynology, organic geochemistry and biomarkers to the reconstructions ofpaleo-environmental history of central Tibet. The new, comprehensive records reveal the history of regional precipitation, temperature and vegetation change in responding to Holocene climatic changesin the region. Organic carbon isotope (δ13C) and lipid n-alkanes were measured from plant samples collected from various altitudes and environments across the study area. The δ13C results indicate the importance of availability of water to C3/C4 herbs distribution in this alpine region. The molecular distributions of trees, shrubs, herbs and submergent macrophytes show distinctive features in a number of indices. These indices are considered to be useful for paleo-environmental reconstructions. A 5.8m-long peat core, which were dated back to 95,000 yr BP was obtained from a river valley at an altitude of 4300 m above sea level. The pollen data from the core reveals a sparse herbaceous vegetation in the catchment area during early Holocene, suggesting non-favourable conditions for vegetation growth. The environment became wetter during the early mid-Holocene around 8100-7000 cal. yr BP, and since then a sedge-dominated wetland habitat was developed. This vegetation changed little until about 1100 cal. yr BP; from which an increase of drought-tolerant herbs was indicated by the pollen data, implying a slightly drier condition of the latter part of late Holocene. The pollen record suggests that the optimum precipitation in central Tibet occurred later and lasted longer than that in the East Asian Monsoon region. Finally, bulk sample carbon geochemistry(TOC, δ13C) as well as the biomarkers analysis on n-alkanes and GDGTs as paleo-limnology and paleo-temperature indicators respectively were applied to the core. Before 1500 cal. yr BP, the wetland was dominated by both vascular herbs as suggested by the δ13Cdata and aquatic floating/submerged macrophytes as indicated by mid-chain n-alkanes. The relative proportion of the two sources of organic matter input varied slightly, and vascular herbs increased in two episodes(5400 -4700 and 2800 -2300 cal. yr BP) indicated by the increase of long-chain n-alkanes (>n-C25). Considering of the soil water content variation by the ratios of iGDGTs to bGDGTs, the change between the two plant communities could to be caused by different lake status. GDGTs paleo-temperature reconstruction indicates a warm period from 6700 to 6000 cal. yr BP, which is believed to be the warmest and highly humid in central Tibetan region. Then the temperature decreased towards the late Holocene, consistent with other paleo climate records across the Plateau region, i.e. largely controlled by change of solar insolation. Along the decreasing trend, a warm episode at about 1200 yr BP that inferred from MAAT was suggested corresponding with the North Hemisphere Medieval Warming. DOI: 10.5353/th_b5270537 Subjects: Paleoecology - Tibet, Plateau of Paleoecology - Holocene

Download or read book Late Quaternary Hydrological Paleoenvironmental and Geomorphological Processes in the Tibetan Plateau and Its Adjacent Areas written by Xiangjun Liu and published by Frontiers Media SA. This book was released on 2022-02-23 with total page 263 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Late Holocene Environmental Change on the NE Tibetan Plateau written by and published by . This book was released on 2005 with total page 382 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Lake Records of Environmental and Climate Change on the Tibetan Plateau written by Zhang Chengjun and published by Frontiers Media SA. This book was released on 2022-11-07 with total page 269 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Late Holocene Environmental Change written by V. N. Panizzo and published by . This book was released on 2010 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Late Glacial to Holocene Climate and Vegetation Changes on the Tibetan Plateau Inferred from Fossil Pollen Records in Lacustrine Sediments written by Yongbo Wang and published by . This book was released on 2011 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The past climate in central Asia, and especially on the Tibetan Plateau (TP), is of great importance for an understanding of global climate processes and for predicting the future climate. As a major influence on the climate in this region, the Asian Summer Monsoon (ASM) and its evolutionary history are of vital importance for accurate predictions. However, neither the evolutionary pattern of the summer monsoon nor the driving mechanisms behind it are yet clearly understood. For this research, I first synthesized previously published Late Glacial to Holocene climatic records from monsoonal central Asia in order to extract the general climate signals and the associated summer monsoon intensities. New climate and vegetation sequences were then established using improved quantitative methods, focusing on fossil pollen records recovered from Tibetan lakes and also incorporating new modern datasets. The pollen-vegetation and vegetation-climate relationships on the TP were also evaluated in order to achieve a better understanding of fossil pollen records. The synthesis of previously published moisture-related palaeoclimate records in monsoonal central Asia revealed generally different temporal patterns for the two monsoonal subsystems, i.e. the Indian Summer Monsoon (ISM) and East Asian Summer Monsoon (EASM). The ISM appears to have experienced maximum wet conditions during the early Holocene, while many records from the area affected by the EASM indicate relatively dry conditions at that time, particularly in north-central China where the maximum moisture levels occurred during the middle Holocene. A detailed consideration of possible driving factors affecting the summer monsoon, including summer solar insolation and sea surface temperatures, revealed that the ISM was primarily driven by variations in northern hemisphere solar insolation, and that the EASM may have been constrained by the ISM resulting in asynchronous patterns of evolution for these two subsystems. This hypothesis is further supported by modern monsoon indices estimated using the NCEP/NCAR Reanalysis data from the last 50 years, which indicate a significant negative correlation between the two summer monsoon subsystems. By analogy with the early Holocene, intensification of the ISM during coming decades could lead to increased aridification elsewhere as a result of the asynchronous nature of the monsoon subsystems, as can already be observed in the meteorological data from the last 15 years. A quantitative climate reconstruction using fossil pollen records was achieved through analysis of sediment core recovered from Lake Donggi Cona (in the north-eastern part of the TP) which has been dated back to the Last Glacial Maximum (LGM). A new data-set of modern pollen collected from large lakes in arid to semi-arid regions of central Asia is also presented herein. The concept of "pollen source area" was introduced to modern climate calibration based on pollen from large lakes, and was applied to the fossil pollen sequence from Lake Donggi Cona. Extremely dry conditions were found to have dominated the LGM, and a subsequent gradually increasing trend in moisture during the Late Glacial period was terminated by an abrupt reversion to a dry phase that lasted for about 1000 years and coincided with the first Heinrich Event of the northern Atlantic region. Subsequent periods corresponding to the warm Bølling-Allerød period and the Younger Dryas cold event were followed by moist conditions during the early Holocene, with annual precipitation of up to about 400 mm. A slightly drier trend after 9 cal ka BP was then followed by a second wet phase during the middle Holocene that lasted until 4.5 cal ka BP. Relatively steady conditions with only slight fluctuations then dominated the late Holocene, resulting in the present climatic conditions. In order to investigate the relationship between vegetation and climate, temporal variations in the possible driving factors for vegetation change on the northern TP were examined using a high resolution late Holocene pollen record from Lake Kusai. Moving-window Redundancy Analyses (RDAs) were used to evaluate the correlations between pollen assemblages and individual sedimentary proxies. These analyses have revealed frequent fluctuations in the relative abundances of alpine steppe and alpine desert components, and in particular a decrease in the total vegetation cover at around 1500 cal a BP. The climate was found to have had an important influence on vegetation changes when conditions were relatively wet and stable. However, after the 1500 cal a BP threshold in vegetation cover was crossed the vegetation appears to have been affected more by extreme events such as dust storms or fluvial erosion than by the general climatic trends. In addition, pollen spectra over the last 600 years have been revealed by Procrustes analysis to be significantly different from those recovered from older samples, which is attributed to an increased human impact that resulted in unprecedented changes to the composition of the vegetation. Theoretical models that have been developed and widely applied to the European area (i.e. the Extended R-Value (ERV) model and the Regional Estimates of Vegetation Abundance from Large Sites (REVEALS) model) have been applied to the high alpine TP ecosystems in order to investigate the pollen-vegetation relationships, as well as for quantitative reconstructions of vegetation abundance. The modern pollen-vegetation relationships for four common pollen species on the TP have been investigated using Poaceae as the reference taxa. The ERV Submodel 2 yielded relatively high PPEs for the steppe and desert taxa (Artemisia Chenopodiaceae), and low PPEs for the Cyperaceae that are characteristic of the alpine Kobresia meadows. The plant abundances on the central and north-eastern TP were quantified by applying these PPEs to four post-Late Glacial fossil pollen sequences. The reconstructed vegetation assemblages for the four pollen sequences always yielded smaller compositional species turnovers than suggested by the pollen spectra, indicating that the strength of the previously-reported vegetation changes may therefore have been overestimated. In summary, the key findings of this thesis are that (a) the two ASM subsystems show asynchronous patterns during both the Holocene and modern time periods, (b) fossil pollen records from large lakes reflect regional signals for which the pollen source areas need to be taken into account, (c) climate is not always the main driver for vegetation change, and (d) previously reported vegetation changes on the TP may have been overestimated because they ignored inter-species variations in pollen productivity

Download or read book Late Holocene Climate Change on the North eastern Tibetan Plateau Reconstructed from Aeolian Sediment Sequences written by Georg Stauch and published by . This book was released on 2016 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Biomarker Based Holocene Climatic Reconstruction in Northwestern China written by Yuxin He and published by . This book was released on 2017-01-26 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: This dissertation, "Biomarker Based Holocene Climatic Reconstruction in Northwestern China" by Yuxin, He, 何毓新, was obtained from The University of Hong Kong (Pokfulam, Hong Kong) and is being sold pursuant to Creative Commons: Attribution 3.0 Hong Kong License. The content of this dissertation has not been altered in any way. We have altered the formatting in order to facilitate the ease of printing and reading of the dissertation. All rights not granted by the above license are retained by the author. Abstract: Holocene hydrological changes in regions influenced by the mid-latitude westerly and the tropical/subtropical Asian monsoon differ from each other. The arid/semi-arid northeastern Tibetan Plateau, lying in between, is very sensitive to climatic changes. It thus becomes a climatologically important region to disentangle the interactions between the two circulations. Yet, limited high-quality Holocene paleoclimatic reconstructions are available in this region. This thesis presents multi-biomarker proxy records from lakes in the Qaidam Basin on the northeastern Tibetan Plateau to investigate the nature of Holocene climate variability. Firstly, late-Holocene paired alkenone-based temperature (U_37 DEGREESK'' ) and moisture (%C37:4) records from Lake Gahai and Lake Sugan were reconstructed. Paired temperature and moisture records confirm the warm-dry (e.g. Medieval Warm Period) and cold-wet (e.g. Little Ice Age) periods on the arid northeastern Tibetan Plateau over the late Holocene, opposite to the warm-wet and cold-dry association in Asian monsoonal regions. The records also suggest substantially warmer and drier conditions during the Medieval Warm Period than the current warm period. Further, a possible link between solar forcing and natural climate variability (both temperature and moisture) during the late Holocene is found on the northeastern Tibetan Plateau. This thesis also studied the late-Holocene grain size-based dust storm history from Lake Gahai to encode possible mechanism of dust storm interacting with hydrological parameters. Intensified dust storm events were identified in periods of 500 BC to 250 BC, 50 BC to AD 250 and AD 1100 to present. In multi-centennial to millennial scales, dust storm events might be caused by the intensified wind induced by strong westerlies or/and Asian winter monsoon. In multi-decadal to centennial scales, moisture and vegetation coverage might have impacted on the dust storm intensity and frequency. Further, Holocene lake level history of Lake Gahai was reconstructed by multiple n-alkane and alkenone proxies. Combined biomarker results provide unambiguous evidence of relatively low lake level at 7-2 ka, probably lowest at 6 ka. Considering the chronological uncertainty, Holocene lake level changes in this marginal region thus display a different pattern from either of the core regions dominated by the westerlies (anti-phase) and the Asian summer monsoon (out-of-phase). The temperature-induced evaporation in the arid marginal region could significantly affect regional hydrological balance, resulting in the discrepancy with the long-term decreasing trend in precipitation in Asian monsoon-dominated regions. Lastly, n-fatty acid δD variation from Lake Hurleg over the past 10.5 ka was investigated. The C26 δD and C16 δD values can indicate water δD changes in terrestrial and aquatic sources, respectively. The heavier C26 δD values during cold and wet conditions suggest that terrestrial water δD changes might be caused by factors other than temperature and moisture, such as glacial melted water input and vegetation type change. The difference between C16 δD and C26 δD was used as an indicator of evaporation at the lake surface. At millennial timescale, less evaporation occurred during cold-wet periods in this region. DOI: 10.5353/th_b5185924 Subjects: Paleoclimatology - China - Tsaidam Basin Paleoclimatology - Ho

Download or read book Late Holocene Climate and Environmental Change Inferred from Arctic Lake Sediment written by Darrell S. Kaufman and published by . This book was released on 2009 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Late Holocene Evironmental Change on the NE Tibetan Plateau written by and published by . This book was released on 2005 with total page 382 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Ostracoda as Proxies for Quaternary Climate Change written by and published by Newnes. This book was released on 2012-12-31 with total page 379 pages. Available in PDF, EPUB and Kindle. Book excerpt: Ostracod crustaceans, common microfossils in marine and freshwater sedimentary records, supply evidence of past climatic conditions via indicator species, transfer function and mutual climatic range approaches as well as the trace element and stable isotope geochemistry of their shells. As methods of using ostracods as Quaternary palaeoclimate proxies have developed, so too has a critical awareness of their complexities, potential and limitations. This book combines up-to-date reviews (covering previous work and summarising the state of the art) with presentations of new, cutting-edge science (data and interpretations as well as methodological developments) to form a major reference work that will constitute a durable bench-mark in the science of Ostracoda and Quaternary climate change. In-depth and focused treatment of palaeoclimate applications Provides durable benchmark and guide for all future work on ostracods Presents new, cutting-edge science

Download or read book Aquatic Ecosystem Response to Late Pleistocene and Holocene Climate Variations written by Sarah Hembrow and published by . This book was released on 2018 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: High resolution palaeoecological data is a valuable tool to determine past climate variability and ecological responses. This thesis examined the aquatic community response of three lakes on Fraser Island using biological and geochemical records for the last 18,000 years. The lake records demonstrate a trend of decreasing precipitation throughout the late Holocene, with increased climatic variability represented by episodic events. From these records, a more detailed knowledge of climate change in eastern Australia during the Holocene has been identified.

Download or read book CRREL Bibliography written by and published by . This book was released on 1998 with total page 656 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Revista espa ola de micropaleontolog a written by and published by . This book was released on 2009 with total page 224 pages. Available in PDF, EPUB and Kindle. Book excerpt: "Numero extraordinario" with 1972.

Download or read book The Anthropocene as a Geological Time Unit written by Jan Zalasiewicz and published by Cambridge University Press. This book was released on 2019-03-07 with total page 385 pages. Available in PDF, EPUB and Kindle. Book excerpt: Reviews the evidence underpinning the Anthropocene as a geological epoch written by the Anthropocene Working Group investigating it. The book discusses ongoing changes to the Earth system within the context of deep geological time, allowing a comparison between the global transition taking place today with major transitions in Earth history.

Download or read book Surface Temperature Reconstructions for the Last 2 000 Years written by National Research Council and published by National Academies Press. This book was released on 2007-01-05 with total page 160 pages. Available in PDF, EPUB and Kindle. Book excerpt: In response to a request from Congress, Surface Temperature Reconstructions for the Last 2,000 Years assesses the state of scientific efforts to reconstruct surface temperature records for Earth during approximately the last 2,000 years and the implications of these efforts for our understanding of global climate change. Because widespread, reliable temperature records are available only for the last 150 years, scientists estimate temperatures in the more distant past by analyzing "proxy evidence," which includes tree rings, corals, ocean and lake sediments, cave deposits, ice cores, boreholes, and glaciers. Starting in the late 1990s, scientists began using sophisticated methods to combine proxy evidence from many different locations in an effort to estimate surface temperature changes during the last few hundred to few thousand years. This book is an important resource in helping to understand the intricacies of global climate change.